Saw-tooth generator with automatic amplitude control



D. E. SUNSTEIN SAW TOOTH GENERATOR WITH AUTOMATIC AMPLITUDE CONTROLFiled Aug. 30, 1944 Aug; 31, 1948.

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INVENTOR.

FME

. Q Maw v Patented Aug. 31, 1948 SAW-TOOTH GENERATOR WITH AUTO- MATICAMPLITUDE CONTROL David E. Sunstein, Elkins Park, Pa., assignor toPhilco Corporation, Philadelphia, Pa., a corporation of PennsylvaniaApplication August 30, 1944, Serial No. 551,949

12 Claims. '(Cl. 250-36) The present invention relates to anautomatically synchronized saw tooth generator, and more particuarly tosuch generator for use as a time axis generator or sweep control for anoscilloscope.

Heretofore cathode ray tubes .or oscilloscopes have been provided foroperation in accordance with a synchronization signal. Where thesynchronization signal is variable in frequency, it has been necessaryto provide a number of manual controls to adjust the operation of thesaw tooth generator. Since considerable skill is required in theadjustment of such manual controls, it has been found desirable toprovide a saw tooth generator which automatically is synchronized torespond to the variations in frequency of the synchronizing or controlvoltage. Accordingly in a co-pending application for an automaticallysynchronized saw tooth generator filed by David E. Sunstein and MillardE. Ames, Jr., Serial No. 551,948, filed August 30, 1944, there isprovided a saw tooth generator which has an automatic amplitude controlto maintain the amplitude of the saw tooth output wave constantindependent of the frequency of operation. In that co-pendingapplication there is disclosed a circuit arrangement wherein a source ofpotential, a capacitor, a charging device and a discharging device for.the capacitor are provided;

one of which has a rapid operating characteristic and the other has avariable operating characteristic. An automatic amplitude controlapplies a control voltage to the device having a variable operatingcharacteristic to maintain constant the amplitude of the output voltage.Such an arrangement is characterized by perfect synchronization over awide range of frequencies from seven cycles per second to seventykilocycles. Substantially constant amplitude is obtained from the rangeof seven cycles per second to fifteen thousand cycles per second. Achange of frequency within that range from the lowest value to thehighest value requires about two seconds to reestablish stability ofoperation. While that arrangement is highly satisfactory for the use forwhich the circuit was intended, certain other applications have shown itdesirable to provide a circuit wherein a lesser amount of time isrequired for the automatic adjustment of the system to a sudden changein the synchronizing frequency. In accordance with the present inventionan improved automatic amplitude control circuit is provided to obtain ashorter response time to sudden changes in the input frequency.

It, therefore, isan object of the present invention to provide animproved automatically synchronized saw tooth generator for a cathoderay tube or an oscilloscope.

It is another object of the present invention to provide an improved sawtooth generator which is automatically synchronized to a control voltageand which is relatively rapid in response to changes in frequency of thecontrol voltage.

Other and further objects of the present invention subsequently willbecome apparent from the following description taken in connection withthe accompanying drawing in which:

Figure 1 is a diagrammatic representation or block diagram illustratingthe present invention;

Figure 2 is a circuit diagram illustrating one manner in which thepresent invention may be constructed; and

Figures 3, 4 and 5 are graphical representations explanatory of theoperation of the circuit in Figure 2.

Referring to Figure 1, there is shown a source of direct current llconnected between ground and a rapid charging device l2 to charge acapacitor l3 which is connected in series with a grounded resistor M. Adischarging circuit is provided for the capacitor i3 which includes avariable discharge device I5 which may have in series therewith a directcurrent meter IS. The voltage appearing across the capacitor I3 as aresult of the operation of the charging and discharging circuits is ofvery nearly constant amplitude over the normal frequency range ofoperation, and hence the direct current meter IE will be deflectedsubstantially directly proportional to the frequency of operation. Thisis brought about by the fact that the charging time of the capacitor I 3is substantially negligible as compared to the discharge time so thatthe direct current meter It will respond to current which issubstantially directly proportional to the frequency of operation, andhence this meter may be used as a frequency meter. An automaticamplitude control I! indicated by a dotted line rectangle controls theoperation of the variable discharge device 15. A pair of outputterminals [8 is connected between ground and one side of the capacitor13. The function of the automatic amplitude control is to adjust therate of discharge of the variable discharge device IS in accordance withthe tendency for changes in the amplitude of the charge to take placewith changes in frequency of discharge. The automatic amplitude controlincludes a number of components indicated by various rectangles andcircuit elements. One of these devices is a slow acting automaticsensitivity control H? which is arranged to control the conductance of avacuum tube forming a portion of the variable discharge device it. Therate of discharge provided by the variable discharge device I5 furtheris also controlledfor each cycle of operation. of the capacitor |3 by acircuit including a capacitor 2| which has one terminal grounded. A veryrapid discharging circuit or device 22 is connected in parallel with thecapacitor 2| to discharge the capacitor at the beginning of eachcharging cycle of the capacitor l3. The capacitor 2| is provided with arapid charging circuit or device 23 which may be controlled from acircuit including a capacitor 24 and a resistor 25 connected betweenground and one side of the capacitor l3. The rapid charging device 23functions to charge capacitor 2| to a degree proportional to the chargeadded to the capacitor |3 by the rapid charging device I 2. The chargeplaced on the capacitor 2| by the charging device 23 is therefore ameasure of the amplitude of the previous saw tooth generated across thecapacitor" l3, and hence may be used to control the rate of discharge ofthe discharge device l5 for the ensuing discharge cycle of capacitor |3.

When the rapid charging device is operating at constant frequency thenthe amplitude of the potential across the capacitor |3 during theensuing discharge cycle can be controlled on the basis of the amplitudeof the potential during the preceding discharge cycle of the capacitorl3. Thus if during the previous discharge cycle of the capacitor l3 thepotential charge was of small amplitude, the charge on the capacitor 2|during the ensuing cycle is small, thereby causing the rate ofdischarge, of the capacitor I3, controlled by the discharge device IE,to be increased through the ensuing cycle. During the ensuing dischargecycle of the capacitor I3, the potential change will be of largeramplitude than the previous cycle. Conversely if during the previousdischarge of the capacitor |3 the potential change was of largeamplitude, then a large charge is placed on the capacitor 2| which ismaintained through-out the ensuing cycle so as to decrease the dischargerate of the discharge device l5, thereby causing a reduction in theamplitude of the potential change during ensuing cycle of the dischargeof the capacitor l3. The automatic amplitude control I"! thus permitsthe rate of operation of the device I5 to be changed with great rapidityso that if the frequency of operation of the rapid charging device I2 issuddenly shifted, the voltage sweep across the capacitor |3 will notexceed or be less than a predetermined value for more than one cycle ofoperation.

One manner in which the various devices indicated by rectangles in theblock diagram of Figure 1 may be constructed is shown by the circuitdiagram in Figure 2. In this figure the reference characters applied tothe various devices indicated by rectangles are directed to the vacuumtubes included in such devices and to the associated circuits. Thepositive terminal of the direct cur-rent source of voltage U of Figure 1has been indicated by the plus sign at various terminals in the circuitof Figure 2.

The rapid charging device for the capacitor |3includes a controlledelectric valve 26 which may be of any suitable type containing a gas orother ionizable medium. A convenient type of tube is a t'hyratron tube884. The grid of the gas substantially tube or controlled electric valve26 is provided with a grounded grid resistor 21 and the grid is coupledby a capacitor 28 to a square wave generator 29. The square wavegenerator is provided with a pair of terminals 3| which may be suppliedwith a suitable synchronizing or signal voltageto initiat'e operation ofthe generator. The square wave generatcrmay comprise any one of a numberof suitable generators, preferably of the peak clipping variety.Alternatively, in stead of a square wave generator, any pulse generatorcould'be employed, but preferably the magnitude of the pulse so formedshould be invariant with changes of signal strength at terminals 3|.

The vacuum tube 26 has a characteristic that whenthe voltage appearingat the grid bears a certain relation to the anode voltage, ionizationtakes place so that current is conducted between the anode and thecathode until a certain voltage condition exists whereby the effectivepotential between the anode and cathode is insufiicient tomaintainionization. When the capacitor |3has become charged, thepotential between the anode and' cathode" of the gas tube 26 is soreduced that ionization cannot be maintained, and the tubebecomesnon-conductive. Conductivity of the tube is initiated by thevoltage supplied by the square-wave generator" 29. After the capacitor|3 has been charged; the variable discharge device |5 dissipate-s thecharge on the capacitor |3'at a controlled rate.

The variable discharge device l5 includes a vacuum tube 32 whichpreferably is'of the pentode type having a characteristic of maintainingconstant: anode current even though" the voltage between the anode andcathodevaries appreciably. The anode of the vacuumtube 32" may beconnected through the direct current meter 5 to one side of the capac--itor 3. The cathode of the vacuum tube 32 is connected to the other sideof the capacitor I3, or directly to ground. The screen grid of thevacuum tube'32 is connected to an intermediate point on the source ofvoltage. A control grid is connected to the negative terminal of asource of potential 33, the positive terminal of which is connected tothe anode of avacuum tube 34. The cathode of the vacuum tube 34 isconnected to the positive terminal of abiasing source of voltage 35, thenegative terminal of which is connected to ground.

The vacuum tube 34 constitutes a polarity reversingstage to'bias thecontrol grid of the vacuum tube 32 negatively during the time that thecapacitor I3 is being charged and to make the control grid more negativewhen a higher potential charge is to be placed on capacitor 2|. The gridof" the vacuum tube 34 is connected to a resistor 36 which in turn'isconnected to a capacitor 2| having one terminal grounded. The grid ofthe vacuum tube 34 is also connected to the positive terminal of asource of biasing potential 38, the-negative terminal of which isconnected to the grid of an electric valve 39. The cathode of the valve39 is connected to the ungrounded terminal of the capacitor 2|. Theanode of the valve 391 is connected to one terminal of a resistor 25,the other terminal of which is grounded.

The electric valve 39 is included in a circuit comprising the device 23for rapidly charging the capacitor 2|. A discharging circuit is providedfor the capacitor 2| which includes an electric valve 4| having an anodeconnected through the resistor 36 tothe capacitor 2|. The

cathode of the electric valve 4| is connected to a positive terminal ofa biasing voltage source 42. The grid of the vacuum tube 4| has agrounded grid resistor 43, and the grid is coupled by at capacitor 44 tothe juncture of resistor M with capacitor Hi. The electric valve 4| andthe associated circuit constitute the rapid discharge de vice 22, forrapidly discharging the capacitor 2|.

The charging circuit for the capacitor 2|, which includes the gas tube39, receives its potential from the capacitor 24 which is interconnectedwith capacitor l3 by an isolation stage. This isolation stage includes avacuum tube 45 which may be of the pentode type having its anode andseveral of its grids connected through a load resistor 50 to the sourceof anode potential. The cathode of the vacuum tube 45 is connected tothe capacitor 24, The grid of the vacuum tube 45 is coupled by acapacitor 46 to one side of the capacitor l3, so that the conductivityof the vacuum tube 45 is determined by the voltage appearing across thecapacitor l3. Hence the voltage supplied through the capacitor 24 to.the electric valve 39 would ordinarily be proportional to the voltageacross the capacitor l3. However, the resistor 25, of relatively smallvalue, in conjunction with the capacitor 24 acts as a difierentiatingcircuit so that anode voltage of the valve 39 is proportional to therate of change of the potential appearing across capacitor I3. The gridof the vacuum tube 45 is connected to a grid resistor 41 which isconnected to another resistor 48. The common juncture between theresistors 41 and 48 is connected to a by-pass capacitor 49 connected tothe cathode of the vacuum tube 45. A voltage divider comprising tworesistors 5| and 52 is connected across the output terminals l8, and thecommon juncture between these resistors is connected to one end of theresistor 48. The isolation stage thus described operates to reduce anyload on the capacitor l3, since such load must be made negligiblecompared to the anode current of the discharge tube 32 if the dischargeis to be maintained substantially linear. A further advantage of theisolating stage is to permit the net resistive component of theimpedance across the capacitor |3 to be maintained at a relatively highvalue so that the capacitor l3 may be of a small size even at lowoperating frequencies. of the capacitor l3 as small 'as possible, thecharging time is maintained at a low value even at the highest audiofrequencies.

Another grid of the vacuum tube 32 is connected to a filter circuitincluding series resistors 53 and 54 and grounded filter capacitors 55and 56. The filter circuit thus described is con? nee-ted to the anodeof a. diode vacuum tube 51.

An anode circuit resistor 58 is connected between ground and the anodeof the diode 51, and the anode is coupled by a capacitor 59 to the anodeof tube 45. The cathode of the vacuum tube 51 is connected to thepositive terminal of a suitable source of biasing voltage 6| so as toprovide the desired degree of delay bias in the operation of the dioderectifier. This delay permits the operation of the vacuum tube 51 to beresponsive only to a potential of sweep amplitude appearing acrosscapacitor IS in excess of a predetermined value. The diode rectifier 51and associated filter and control circuit components therefor comprisethe slow acting automatic sensitivity control l9 used to adjust thesensitivity of discharge device |5 so as to maintain a constant Bymaintaining the size amplitude output at the terminals l8, as shown inFigure 3.

'It may be assumed now that a signal or control voltage is applied tothe terminals 3| of the square wave generator 29 thus causing thisgenerator to supply to the grid of the electric valve 26 a positivepotential. The positive potential produces ionization so as to renderthis valve conductive so that the capacitor I3 is new connected in acharging circuit which includes the resistor I4. T-he resistor M has arelatively low value so as not to render the rate of charge of thecapacitor l3 excessively great and yet the value of resistor i4 must besufficient to supply the necessary voltage to initiate operation of theelectric valve 4|.

The initiation of the conductivity of the electric valve 26 generates a.voltage drop across the resistor M which is applied through the couplingcapacitor 44 to the control grid of the electric valve 4|. The electricvalve 4| is arranged to discharge the potential appearing across thecapacitor 2| to a predetermined value. The change in voltage producedacross the resistor 36 by the discharge of the capacitor 2| applies apotential to the control grid of the electric valve 39 so as to renderthis valve non-conductive. The increase of potential appearing acrossthe capacitor |3 which is being charged is transmitted through theisolation stage including the vacuum tube 45 to the capacitor 24 so thatthe charging circuit including the electric valve 39 will charge thecapacitor 2| to a voltage directly proportional to the change in voltageproduced across the capacitor |3 by electric valve 26.

When the charge being developed across the capacitor l3 increases to acertain value, the potential appearing between the anode and the cathodeof the electric valve 26 is insufficient to maintain ionization so thatthe valve then becomes non-conductive. Similarly, as the capacitor 2| ischarged to a certain value, the potential appearing between the cathodeand anode of the electric valve 39 becomes insufficient to supportionization so that this valve becomes non-conductive. The capacitor 2|therefore now has a certain potential thereon which potential isutilized to control the rate of discharge of the discharging circuit forthe capacitor l3. The potential appearing on the capacitor 2| is appliedthrough the resistor 36 to the grid of the polarity reversing vacuumtube 34 so as to reduce by the desired amount the negative biasingappearing at the control grid of the discharging vacuum tube 32. Uponcompletion of the discharge of the capacitor |3 at a rate as determinedby the operation of the vacuum tube 32, the apparatus is then again incondition to repeat the previously described cycle of operation.

Each time, the capacitor 2| is very rapidly discharged by the electricvalve 4| and then charged by the electric valve 39 to a voltage directlyproportional to the charge being placed on the capacitor l3. If thefrequency of operation of the square wave generator 29 is varied inaccordance with the change in the frequency of the control signalapplied to the terminals 3|, it will be appreciated that any variationproduced in the charge across the capacitor I3 will be corrected in onecycle of operation. Thus there has been provided a circuit which canfollow with rapidity any changes in the frequency of the input signaleven though such changes are over wide ranges and are made suddenly.

Proper operation will be achieved only when the 1'7 variable dischargedevice I including the vacuum tube 32 is operated in accordance with agiven and proper relationship between the rate of discharge and theamplitude of applied controlling signal supplied by the capacitor 2|.Let it be assumed that a condition of operation exists in which thecharging device I2 is operating at constant frequency and in which thetube 32 of variable discharge device I5 is overly sensitive, i. e., inwhich the rate of discharge varies too much for changes in controllingsignal from the capacitor 2|. Then the wave form of the voltage acrossthe capacitor l3 will appear as in Figure 4, instead of as in Figure 3which represents proper operation resulting when variable dischargedevice |5 has proper sensitivity. In Figure 4 the capacitor 13 ischarged over portion III of the curve by the rapid charging device l2.Then let it be assumed that the capacitor I3 is discharged rapidly overthe portion ll of the curve thereby causing a large amplitude ofdischarge up to the time indicated by point 12. At the time indicated bypoint 12, the rapid charging device I2 is again operated to chargecapacitor I3 over the portion '13 of the curve. discharge H was of largeamplitude, the capacitor 2| receives a large charge by the time thatcurve 13 reaches the point 14. Since it is assumed that the vacuum tube32 of the variable discharge device [5 is overly sensitive, this largecharge on the capacitor 2| causes the ensuing discharge cycle 15 of thecapacitor l3 to be made at a very slow rate, resulting in smallamplitude of discharge up to the time 16. The capacitor 2| then isdischarged and it receives a small charge 'because of the fact that thecycle 15 was of small amplitude. This will cause the ensuing cycle 18 tobe of even greater amplitude than cycle thereby causing cycle I9 to beof even less amplitude than cycle 15, etc. Thus a condition ofoscillation is established if variable discharge device I5 is overlysensitive.

If it is assumed that the vacuum tube 32 of the variable dischargedevice I5 is under sensitive, the output wave appearing across thecapacitor [3 will be similar to that shown in Figure 5, in which stableequilibrium is reached after many cycles, but at very small amplitude.

In order to maintain the sensitivity of the variable discharge device l5at the particular value for proper operation represented by Figure 3,the slow acting sensitivity controllS is included which adjusts thesensitivity of discharge device in accordance with the average amplitudeof several preceding cycles of discharge. Thus if the average peakamplitude of the discharge is large, the sensitivity control [9 acts toreduce the sensitivity of the variable discharge device I5. Conversely,if the average peak amplitude of discharge is small, the sensitivitycontrol IS increases the sensitivity of the variable discharge device15. Thus operation with the proper sensitivity of the variable dischargedevice I5 is insured so that the output wave will be as in Figure 3 forthe case of constant frequency operation of the charging device l2.

The ability of the circuit shown in Figure 2 to follow rapid or greatchanges in the frequency of operation as determined by the controlsignal applied to the terminals 3|, is dependent upon a particulartransconductance value for the vacuum tube 32. This transconductancevalue, which is the ratio of the change in plate current compared to thecontrol grid voltage producing the change, is directly related to theratio of the Since the discharge current of the vacuum tube 32 com-'pared to the voltage appearing across the capacitor 2|. Thisrelationship must have a particular value since if the transconductanceis too small, then each successive saw tooth of the output appearingacross the terminals l8 will be decreased in amplitude as in Fig. 5. Ifthe transconductance is too large, the eiiect will be as in Fig. 4.While the transconductance of the vacuum tube 32 may be controlled by amanually adjustable control, thus adjustment is rather critical and isobviated by the provision of a slow acting automatic sensitivitycontrol. Therefore, the operation of the vacuum tube 51 is such as tocontrol the transconductance of the vacuum tube 32 according to theaverage amplitude of several successive saw tooth voltages appearingacross the output terminals IS. The capacitor 59 is connected to theungrounded terminal of the grounded resistor 53 so that a potential isdeveloped across this resistor porportional to the saw tooth voltagesappearing across the output terminals. The cathode of the vacuum tuberectifier 53" has been provided with a small positive bias to providethe desired degree of delay. The voltage appearing across the resistor58 is developed by voltages obtained from a plurality of successive sawtooth voltages at the output terminals. When the anode end of theresistor 58 exceeds a certain voltage value, the diode rectifier 57 willbecome conductive to a greater degree thereby modifying the voltagebeing supplied through the filter network including the resistors 53 and54 and the capacitors 55 and 56 'to one of the grids of the vacuum tube32. A variation of the voltage supplied to this grid of the vacuum tube32 controls the transcondu-ctance of the tube in accordance with theaverage of several saw tooth voltages appearing in succession across theoutput terminals 18.

While for the purpose of explanation and illustration of the presentinvention, there has been shown in the drawing a certain arrangementembodying the present invention, it is to be understood that theinvention is not to be limited thereby since obviously other circuitarrangements may be provided, and such variations in the circuitarrangements and in the instrumentalities employed are contemplated asmay be commensurate with the spirit and scope of the invention "as setforth in the appended claims.

This invention is hereby claimed as follows:

1. The combination comprising a source of unidirectional current, anenergy storage device, a charging device for charging said storagedevice from said source, a discharging device for said storage device,and means responsive to the magnitude of the voltage of each charge ofsaid storage device for controlling the rate of discharge of saiddischarging device.

2. The combination comprising a source of unidirectional current, anenergy storage device, means for charging said device from said source,means for discharging said device at a controlled rate, means responsiveto a signa1 voltage for controlling the operation of said chargingmeans,

and means responsive to the magnitude of the charge supplied to saiddevice for modifying the rate of discharge of said discharging means,and an output circuit arranged to be energized by said device.

3. The combination comprising a source of unidirectional current, anenergy storage device, a circuit for rapidly charging said device fromsaid source, a circuit for discharging said device at a controlled rate,an output circuit arranged to be energized by said device, meansoperating on each cycle of said charging circuit to determine the rateof operation of said discharging circuit, and means for furthermodifying the rate of operation of said discharging circuit inaccordance with the value of the output potential appearing across saidoutput circuit averaged for a plurality of cycles.

4. The combination comprising a source of di rect current, an energystorage device, a circuit for rapidly charging said device from saidsource, a discharging circuit for said device, said discharging circuitincluding a vacuum tube having a control circuit including an energystorage device responsive to the maximum voltage of the charge appearingacross said first device to control the rate of discharge of said firstdevice.

5. The combination comprising a source of 'direct current, an energystorage device, a circuit for rapidly charging said device from saidsource, and a circuitfor discharging said device at a controlled rate,said discharging circuit includ-- ing a vacuum tube, means for varyingthe transconductance of said vacuum tube in accordance with the averagevalues of a plurality of successive values appearing across said device,and means for modifying the conductivity of said vacuum tube inaccordance with the magnitude of each charge of said device.

6. The combination comprising a source of direct current, a capacitor, acircuit for rapidly charging said capacitor in response to a controlsignal, a discharging circuit for said capacitor including a vacuumtube, an output circuit arranged to be energized by said capacitor,means for varying the transconductance of said vacuum tube in accordancewith the average values of a plurality of successive potentialsappearing across said output circuit, a control circuit for said vacuumtube for controlling the rate of discharge of said capacitor inaccordance with the value of each charge appearing across said capacitorincluding a second capacitor arranged to receive a charge proportionalto the charge supplied to said first capacitor by said circuit forrapidly charging said first capacitor.

7. The combination comprising a source of direct current, a capacitor, acircuit for rapidly charging said capacitor from said source, and acircuit for discharging said capacitor at a controlled rate, saiddischarging circuit including a vacuum tube having a control circuitincluding a second capacitor for supplying potential thereto, means fordischarging said second capacitor While said first capacitor is beingcharged, and means for charging said second capacitor to a voltageproportional to the charge across said first capacitor while said firstcapacitor is being charged.

8. The combination comprising a capacitor. a source of unidirectionalcurrent for rapidly charging said capacitor, a discharging circuit forsaid capacitor including a vacuum tube having a control circuit formodifying the rate of discharge in accordance with the magnitude of thecharge appearing across said capacitor, said control circuit including asecond capacitor, a discharge circuit for said second capacitor arrangedto be responsive to the initiation of the charging cycle of said firstcapacitor, and a charging circuit for said second capacitor arranged torapidly charge said second capacitor during the charging period of saidfirst capacitor to a voltage proportional to the charge placed upon saidfirst capacitor by said source of unidirectional current.

9. A sawtooth wave generating system, comprising a capacitor, meansresponsive to a synchronizing signal for charging said capacitor, meansfor discharging said capacitor, whereby to generate a sawtooth wave, andmeans responsive to the magnitude of the charge on said capacitor duringeach charging cycle for varying the rate of discharge of the capacitor,so as to maintain synchronization over a range of frequencies of saidsignal and to maintain the amplitude of the generated sawtooth wavesubstantially constant.

10. A sawtooth wave generating system, comprising a capacitor, meansresponsive to a synchronizin signal for charging said capacitor, meansfor discharging said capacitor, whereby to generate a sawtooth wave, asecond capacitor, means for charging said second condenserproportionately to the charge on said first capacitor, and meansresponsive to the charge on said second capacitor for varying the rateof discharge of said first capacitor, so as to maintain synchronizationover a range of frequencies of said signal and to maintain the amplitudeof the generated sawtooth wave substantially constant.

11. A sawtooth wave generatin system, comprising a capacitor, meansresponsive to a synchronizing signal for charging said capacitor, meansfor discharging said capacitor, whereby to generate a sawtooth wave,said discharging means including a controllable device whose sensitivitymay be varied, means responsive to the magnitude of the charge on saidcapacitor during each charging cycle for controlling said device so asto control the rate of discharge of the capacitor, to thus maintainsynchronization over a range of frequencies and also to maintain theamplitude of the generated sawtooth wave substantially constant, andmeans for controlling the sensitivity of said device in accordance withthe average voltage across said capacitor during a number of cycles.

12. A sawtooth wave generatin system, coInprising a capacitor, means foralternately chargin and discharging said capacitor to produce a sawtoothvoltage wave in response to a synchronizing signal, a second capacitor,means responsive to each cycle of the sawtooth Wave for charging anddischarging said second capacitor, and means controlled by said secondcapacitor for controlling the amplitude of said sawtooth wave so as tomaintain synchronization over a range of frequencies of said signal andto maintain the amplitude of said wave substantially constant,

DAVID E. SUNSTEIN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,102,951 Hackenberg Dec. 21,1937 2,126,243 Busse Aug. 9, 1938 2,153,217 Mark Apr. 4, 1939 2,167,496Bauer July 25, 1939 2,180,365 Norton Nov. 21, 1939 2,227,815 Toulon Jan.7, 1941 2,265,290 Knick Dec. 9, 1941 OTHER REFERENCES A. P. C.Application of De France, Serial No. 464,750, published June 8, 1943.

